1. Field of the Invention
The present invention relates to a device for suspending a turbine engine such as a turbojet from a portion of an airplane.
2. Description of the Related Art
Conventionally, a turbojet comprises a plurality of casings in alignment and surrounding, from upstream to downstream: low and high pressure compressors; a combustion chamber; and high and low pressure turbines. The downstream end of the turbojet has an exhaust casing for exhausting the gas burnt in the combustion chamber. The outside surface of this casing includes means for suspending or attaching the turbojet to a portion of the airplane. These suspension means include clevises, each of which comprises two lugs having orifices in alignment for passing a shouldered pin that, in-between the lugs, passes through a member providing connection to a portion of the airplane.
In order to hold the shouldered pin inside the orifices of the lugs of the clevis, a nut is screwed onto one end of the shouldered pin, and at its end opposite from the nut, the pin has a projecting annular rim placed against the clevis. The fastener nut and the annular rim form abutments for axially retaining the shouldered pin in the clevis. In operation, the outside faces of the lugs of the clevis come into contact with the nut and with the annular rim, thereby leading to wear of the outside faces of the lugs of the clevises. This wear gives rise to grooves or furrows being formed in the outside faces of the lugs.
In order to avoid subjecting the outside faces of the lugs to wear, the Applicant has already proposed, in document FR 2 923 460, interposing respective antirotation washers between the outside faces of the lugs and the fastener nut at one end and the annular rim at the other end. Nevertheless, in operation, the clevises transmit thrust forces to the airplane and they are subjected to high levels of vibration, and it is found that the washers do not perform their antirotation function correctly, being subjected to repeated movements in rotation that wear the outside faces of the lugs. That type of movement of the washer is known as “fretting”.
It is possible to carry out a repair by performing a grinding operation on the worn outside faces of the lugs. Such an operation consists in smoothing the outside faces of the lugs by means of an abrasive member put into rotary contact with the outside faces of the lugs. Nevertheless, such an operation can be performed only a limited number of times since it removes material from the lugs of the clevises. This results in a reduction in the thickness of the lugs and thus in their mechanical strength, and it also increases the clearance between the lugs and the abutments. Furthermore, the faces of the lugs that are restored in this way will continue to wear in operation.
This grinding operation requires the turbine engine to be removed, thereby increasing the length of time it is out of service and thus increasing the cost of operating the airplane. Finally, it is possible to perform grinding only when the depth of the wear is relatively shallow, being of the order of 0.1 millimeters (mm) to 0.2 mm, which requires the lugs of the clevises to be inspected regularly in order to be carry out the grinding before the wear has become excessive. When the wear is greater than about 0.5 mm, the casing must be replaced as a whole.
Given the regulations that are in force, it is not possible to envisage building up the outside faces of the lugs by tungsten inert gas (TIG) deposition.